To be a member of the SSA you must also be a member of the ISF and have an athlete's card, here is the link

The method for becoming an official member of the SSA is under development

MEMBERS: (ATHLETES, ORGANIZERS,SUPPORTER)

Currently anyone can support the SSA. 

All athletes participating in official international competitions are selected by the organising committee.

For more information write at: info@swiss-skyrunning.ch